There are process inks, medium pigmented inks and heavily pigmented inks. The main difference is the percentage of pigment in the ink. Process inks have the least amount of pigment, and therefore are transparent and need to be printed on white garments. They stir very easily in the can and typically have a soft feel, or “hand,” when printed. Medium pigmented inks are designed for white and light colored garments. The ink needs to be darker in color than the garment to have opacity. These inks also stir relatively easily. Of the inks Union Ink makes, examples are UltraSoft and Unimatch inks.
Heavily pigmented inks are designed for dark garments and special applications like athletic printing, printing on polyesters, and 3-D printing. These inks can be difficult to stir in the can. Knowing how to modify these inks to make them “friendly” is important.
There are four ways to convert inks to “friendly” status. First, stir the ink vigorously. Some companies sell ink mixing machines for this purpose. A variable speed hand drill with spade drill bit turning slowly will serve the same purpose without the same investment. The ink can must be secured, such as by a vice, to prevent spinning, and cardboard should be placed over the top to prevent ink from flying all over the room. The thorough mixing of the ingredients will make the ink easier for printing.
The second method is blending. Here two inks of the same color are first mixed thoroughly as described above, and then put in a separate container in a ratio of 75-80% of the heavily pigmented ink to 20-25% of the medium pigmented ink. That dilutes the pigment in the ink without changing the chemical balance of the ink. This method is recommended for dark garments, because typically there is no lose of opacity.
The third method is adding “soft hand” which is known by other various names like soft hand clear, and Shape (a brand name of a particular ink company). This is ink without pigment. When printed alone on a garment, soft hand is transparent. Sometimes shops will print soft hand as an underbase to control a fibulation problem that sometimes occurs with cotton garments. Stir the soft hand, and you will find it stirs very easily. That is because there is no pigment. When soft hand is added to a pigmented ink, the pigment is diluted making the ink easier to stir and less opaque. This method is not recommended for dark garments.
The last method is commonly abused in the screen printing industry. That is adding “curable reducer” which is a diluted form of plasticizer. We know that plasticizer is one of the three basic ingredients of plastisol inks. “Curable” simply means some amount of PVC as been added to make the plasticizer less potent. The PVC gives the curable reducer a white look.
Curable reducer reduces the co-adhesive factor of ink. When applied in excess, the ink will not stand up on the surface of the garment. Curable reducer should not be used in technical printing like process printing, because the half tone dots will suffer dot gain. This product is abused, because almost without exception all screen printers add sufficient quantities of curable reducer to make the ink pass through the screen easier. There are many ways to get ink to pass through a screen easily, and curable reducer is not one of the acceptable methods. Instead, a minute quantity, such as 3 drops per quantity of ink that will go in a screen should only be added, and then very thoroughly mixed into the ink to disperse that minute quantity equally through the entire volume of ink going into the screen. The purpose of this small quantity of curable reducer is to help the ink shear from the bottom of the screen.
Ink is ideal for printing when it shears easily. Stir yogurt in a cup with a spoon, and pull the spoon out of the cup. Notice how the yogurt on the spoon and in the cup separate. That is ideal shear. Now repeat the process with a medium pigmented ink that has been thoroughly stirred, and the experience will not be exactly the same, but close. By contrast, stir a heavily pigmented ink and see how the ink separates. The ink will be more like taffy. You might be able to get the stir stick 6” above the can before the ink in the can and on the stick separate. Such inks are difficult to get through the screen leading to slower production, more labor and risk of developing carpel tunnel syndrome.
Ideal ink balances the requirement of opacity and releasing ink easily and completely from the screen. The 3 drops of curable help ink release, but too much curable reducer, and the shape and thickness of the ink deposit that was formed by the image in the stencil will collapse. Polyester mesh and stencil are very slippery. Just feel them, and you will know there is no surface condition to retain ink on the surface of polyester threads or the stencil. Vigorous stirring and the blending method are the best ways to create ideal ink for printing.
Other risks with curable reducer include the ink not curing and dye migration being created. If too much is added to the ink, the ink might never cure properly. That means the ink will wash out of the garments. Dye migration typically occurs with synthetic fabrics like 50-50% shirts, blended sweatshirts, or any synthetic fabric. You will know when you have dye migration, because the ink color will be tinted by the color of the fabric. The highest risk colors of fabrics are red, maroon and green. Low bleed inks like the polyester series should be used and other precautions taken to avoid a job turning sour.
For additional information on this subject, see:
“Making Inks Friendly”
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